The present invention relates generally to cooling hole airflow of gas turbine engine components, and more particularly to a method of adjusting cooling hole airflow.
Cooling holes are formed in many gas turbine components for transporting film cooling air through the component to cool the component and to form a fluid barrier between the component and hot gases traveling through a main flowpath of the engine. In addition, some components such as combustion chamber centerbodies are coated with a corrosion inhibiting coating by a conventional flame spray process to prevent the centerbodies from being corrosively attacked by the hot gases traveling through the combustion chamber. The centerbodies are also coated with a thermal barrier coating by a conventional physical vapor deposition process to insulate the centerbodies. After a period of service, the centerbodies are removed from the engine for replacement or repair.
During repair, the corrosion inhibiting coating, thermal barrier coating and contaminants (e.g., combustion products) are removed from the centerbodies by a conventional acid strip process. The strip process removes the coating and contaminants, as well as some base material resulting in the cooling holes being enlarged. Following structural inspection, the centerbodies are recoated with a corrosion inhibiting coating and then recoated with thermal barrier coating. The coated centerbodies are flow checked to determine if the cooling hole airflow is within preselected limits. If the centerbodies pass the flow check, they are returned to service. In the past, no procedure was available to correct airflow if the centerbodies did not pass the flow check during repair or during initial manufacture.
Among the several features of the present invention may be noted the provision of a method of adjusting airflow through a plurality of cooling holes by depositing a thermal barrier coating on an exterior surface and/or an interior surface of the component by a physical vapor deposition process. The cooling holes are not masked. Thus, a portion of the thermal barrier coating partially obstructs airflow through the cooling holes and reduces airflow through the cooling holes. A predetermined pressure drop is developed across the cooling holes and airflow through the cooling holes is measured. The measured airflow is compared to a preselected range of desired cooling hole airflows and the steps of depositing the thermal barrier coating, developing the predetermined pressure drop, calculating airflow and comparing the measured airflow to the preselected range are repeated until the measured airflow is within the preselected range of desired cooling hole airflows.
In another aspect, the method of the present invention includes the steps of selecting a period of time during which to deposit a second thermal barrier coating based on the measured airflow so airflow through the cooling holes after depositing the second thermal barrier coating is within a preselected range of cooling hole airflows. The second thermal barrier coating is then deposited for the selected period of time.
In yet another aspect, the method of the present invention includes the steps of developing a predetermined pressure drop across the cooling holes and calculating airflow through the cooling holes resulting from the predetermined pressure. The method also includes the step of selecting a period of time during which to deposit a thermal barrier coating based on the measured airflow through the cooling holes so airflow through the cooling holes after depositing the thermal barrier coating is within a preselected range of cooling hole airflows. The thermal barrier coating is deposited on either the exterior surface or the interior surface of the component for the selected period of time by a physical vapor deposition process without masking the cooling holes. Thus, a portion of the thermal barrier coating partially obstructs airflow through the cooling holes and reduces airflow through the cooling holes thereby obtaining airflow through the cooling holes within the preselected range of cooling hole airflows.
Further, the present invention includes a gas turbine engine component comprising a body having a plurality of cooling holes therein. The component has a plurality of layers of thermal barrier coating extending over at least a portion of an interior surface and/or an exterior surface of the component. Each layer of thermal barrier coating at least partially obstructs airflow through the cooling holes to reduce airflow through the cooling holes.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.